Automatic sorting systems are generally utilized to sort unacceptable material from a product stream. For example, in the context of agricultural products, a product stream may be sorted to separate rocks, debris and unsatisfactory fruits, vegetables, tobacco and other unacceptable material from acceptable product. Similarly, automatic sorting systems are employed to separate unacceptable material from streams of wood chips, plastic materials and a variety of other commercial products.
Generally, such automatic sorting systems include a detector, such as a digital camera, for identifying unacceptable material and a sorting element for diverting the unacceptable material from the product stream, for example, mechanically or by using a compressed air blast. Ideally, the product stream is thereby bifurcated into a reject bin including only unacceptable material and an accept bin including only acceptable product. The overall effectiveness of a sorting system may be determined based on both accuracy (errors per quantity) and throughput (quantity per unit time).
Errors result from a number of factors. The case of sorting a wood chip stream using compressed air blasts is illustrative in this regard. The wood chip stream is typically transported through the inspection zone of the sorter at a high rate of speed. Additionally, the stream is typically distributed in an irregular or random pattern across the length and width of the belt, and unacceptable material is therefore often located in close proximity to acceptable product. Although the air blasts are closely controlled in order to minimize the potential for error, such blasts are finite in duration and disperse over distance. As a result, air blasts intended to divert unacceptable material from the product stream may also divert acceptable product thereby reducing yield. Similar problems are presented in a variety of other sorting applications.
In order to manage such error, operators commonly manipulate a number of system parameters such as operating speed and system geometry in order to achieve a balance of accuracy and throughput that is acceptable for each particular sorting application. In applications where very high purity is desired, e.g., sorting debris from food products, the system may be adjusted to sacrifice yield in favor of purity. However, this may result in waste. Where purity is less critical, e.g., sorting wood chips, the system may be adjusted to enhance throughput at the expense of purity. In many applications, achieving the desired product quality requires reducing throughput to levels where the financial viability of the sort is threatened. The continued and enhanced viability of automatic sorting systems for many applications depends on the ability to achieve high accuracy at high throughput levels.